Theregoes: you can start and attend whenever you can, it's a rolling programme, so talk to them and see if something can be worked out.
Failing that, can you find a way to arrange child care for the future. Is there a drop in creche anywhere near? can you ask the organisers, they may be able to suggest a childminder that could take them for the couple of hours?
You really do need to do this programme, it will help you.
I think you also need to face facts that your mum is not going to be the most useful of supports in this. You need to minimise the reliance on her.
It's horrid to have to face this, but I had to, I don't talk about pretty much anything with her, no point.
You have us, that's a start....